Ultrasonic imaging is a method for imaging the interior structure of a living body, such as a human body, by transmitting ultrasonic into a human body and receiving echoes reflected from interfaces between tissues and organs having different acoustic characteristic impedances and imaging them based on the received echoes.
A bmode ultrasonic diagnosis device scans a living body one dimensionally with ultrasonic beams transmitted from a probe so as to image a cross section of tissues or organs being scanned. On the displayed cross section, brightness of points indicates amplitudes of echo signals (lighted points), X-axis demonstrates a distance over which the ultrasonic beams scan, and Y-axis demonstrates a detected depth into the tissues or organs.
A conventional mmode ultrasonic diagnosis device which provides images of time-motion type is generally used for observing the motion of a heart. In an operating status, a probe transmits ultrasonic beam from a fixed position and in a certain direction and receives the echo signals. On a mmode display, the brightness of each point constituting the display is proportional to the amplitude of the echo from the depth represented by the point. The Y-axis coordinate of each point represents the depth into a heart, for example, and the X-axis coordinate indicates time at which the data for that point is measured. Therefore, a mmode display shows traces of movement of tissues of a heart.
Modern ultrasonic diagnosis devices often show bmode and mmode together on the same display. By defining positions that need to be detected by a mmode probe on a bmode cross-section display, and detecting along the defined positions with a mmode probe, desired mmode images are obtained.
However, during a conventional mmode imaging process, due to the presence of lung or ribs, it's difficult to orient the ultrasonic beam transmitted from a probe to be normal to the wall of the heart being detected, which will deteriorate the accuracy of the resultant data; further, the heart cannot keep being in a constant angle from the ultrasonic beam, as a result, the echo signal from a same position on the surface of the heart has a varying intensity, that is, the displayed trace of movement of the surface of the heart has varying brightness, which in the worst cases might negatively affect judgment of a medicine doctor.
A patent application U.S. Pat. No. 6,589,175 B2 by PHILIPS discloses a mmode ultrasonic imaging method and apparatus, in which ultrasonic beams are transmitted and echoes are received to form conventional mmode images in the time intervals of producing a plurality of frames of bmode images, inevitably it will occupy the time originally for producing bmode images. To some extent, the method and apparatus overcome the above-mentioned defaults of conventional mmode images, however it lowers the frame rate of bmode images, and obviously degrades the performance of apparatuses having low frame rate of bmode images.
Recently there is introduced an anatomical mmode or arbitrary mmode ultrasonic imaging method and apparatus. In this method, based on a sample line defined by a user on a displayed bmode image, bmode data (i.e., detected depth of echo signals and brightness corresponding to the amplitudes of the echoes) corresponding to each sample point included in the sample line are selected from each frame of bmode image. Then convert the bmode data selected from each frame of bmode image into a mmode line corresponding to a certain time in a mmode image, so as to produce a plurality of mmode lines arranged in time order to show the traces of movement of the interfaces that the sample line goes across.
However, in the case that the bmode images are measured at low frame rate, when producing anatomical mmode images from the bmode data, there will be a relatively big interval between adjacent mmode lines in a mmode image, as a result, the traces displayed in a mmode image are not continuous visually. This is not satisfying for observing organs such as a heart that moves fast.